U.S. patent number 5,657,231 [Application Number 08/427,818] was granted by the patent office on 1997-08-12 for route setting method and route setting apparatus in navigation system, and navigation system.
This patent grant is currently assigned to Pioneer Electronic Corporation. Invention is credited to Morio Araki, Kenichi Nobe.
United States Patent |
5,657,231 |
Nobe , et al. |
August 12, 1997 |
Route setting method and route setting apparatus in navigation
system, and navigation system
Abstract
A route setting method in a navigation system for obtaining a
shortest route from a starting position to a destination position,
includes the steps of: selecting, out of links each corresponding
to a partial route connecting two route positions adjacent to each
other on a route, candidacy links each connected to one of
confirmed links which include a link corresponding to the partial
route connected to the starting position and which have been
confirmed; judging whether or not each of the candidacy links
selected by the selecting step is able to pass therethrough
according to link judgement information, which corresponds to a
connection relationship between each of the candidacy links and the
confirmed link connected to each of the candidacy links and which
is set in advance; confirming one of the candidacy links judged to
be able to pass therethrough by the judging step, which has the
shortest integrated route distance from the starting position, as a
new confirmed link; and repeating the selecting, judging and
confirming steps with respect to the confirmed links including the
new confirmed link confirmed by the confirming step.
Inventors: |
Nobe; Kenichi (Kawagoe,
JP), Araki; Morio (Kawagoe, JP) |
Assignee: |
Pioneer Electronic Corporation
(Tokyo-to, JP)
|
Family
ID: |
14022082 |
Appl.
No.: |
08/427,818 |
Filed: |
April 26, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Apr 28, 1994 [JP] |
|
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6-091281 |
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Current U.S.
Class: |
701/428; 340/990;
340/995.19; 701/533 |
Current CPC
Class: |
G01C
21/34 (20130101) |
Current International
Class: |
G01C
21/34 (20060101); G01C 021/00 (); G06G
007/78 () |
Field of
Search: |
;364/443,444.2,444.3
;73/178R ;340/988,990,995 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Chin; Gary
Attorney, Agent or Firm: Young & Thompson
Claims
What is claimed is:
1. A computer-implemented method in a navigation system for
obtaining a shortest route via a plurality of positions,
interconnected by a plurality of links, from a starting position to
a destination position, wherein each of said plurality of links
connects two said positions and has an associated length, said link
information being stored in a memory accessible by said computer,
comprising: using a computer, performing the steps of:
choosing, using said computer, a confirmed link from amongst said
plurality of links which are connected to said starting position,
said confirmed link having a shortest said associated length;
selecting, using said computer, candidacy links from said plurality
of links, said candidacy links being connected to at least one said
confirmed link at one of said plurality of positions;
judging, using said computer, whether or not each of the candidacy
links selected by said selecting step is allowable according to
link judgement information, said link judgement information
including a connection relationship between each of the candidacy
links and the confirmed link connected to each of the candidacy
links, said link judgement information being set in advance;
confirming, using said computer, one of the candidacy links judged
to be allowable by said judging step, said confirmed link having a
shortest integrated route distance from the starting position;
and
repeating said selecting, judging and confirming steps with respect
to the confirmed links until said shortest route is determined, and
reporting said shortest route to a user.
2. A method according to claim 1, further comprising the step of
storing the link judgement information into a memory device.
3. A method according to claim 1, wherein the link judgement
information comprises an information flag which indicates whether
or not each of the links in the corresponding connection
relationship is allowable under a traffic regulation thereof.
4. A route setting apparatus in a navigation system for obtaining a
shortest route via a plurality of positions, interconnected by a
plurality of links, from a starting position to a destination
position, wherein each of said plurality of links connects two said
positions and has an associated length, comprising:
a choosing means for choosing a confirmed link from amongst said
plurality of links which are connected to said starting position,
said confirmed link having a shortest said associated length;
a selection means for selecting candidacy links from said plurality
of links, said candidacy links being connected to at least one said
confirmed link at one of said plurality of positions;
a judgement means for judging whether or not each of the candidacy
links selected by said selecting step is allowable according to
link judgement information, said link judgement information
including a connection relationship between each of the candidacy
links and the confirmed link connected to each of the candidacy
links, said link judgement information being set in advance;
and
a confirmation means for confirming one of the candidacy links
judged to be allowable by said judgement means, said confirmed link
having a shortest integrated route distance from the starting
position, said selection means selecting said candidacy links from
said confirmed links.
5. An apparatus according to claim 4, wherein said judgement means
comprises a memory means for storing the link judgement information
in advance.
6. A method according to claim 4, wherein the link judgement
information comprises an information flag which indicates whether
or not each of the links in the corresponding connection
relationship is allowable under a traffic regulation thereof.
7. A navigation system for a movable body comprising:
a route setting apparatus for obtaining a shortest route via a
plurality of positions, interconected by a plurality of links, from
a starting position to a destination position, wherein each of said
plurality of links connects two said positions and has an
associated length, and
a guidance means for generating a message to guide said movable
body from the starting position to the destination position on the
basis of the shortest route obtained by said route setting
apparatus,
said route setting apparatus comprising:
a choosing means for choosing a confirmed link from amongst said
plurality of links which are connected to said starting position,
said confirmed link having a shortest said associated length;
a selection means for selecting candidacy links from said plurality
of links, said candidacy links being connected to at least one said
confirmed link at one of said plurality of positions;
a judgement means for judging whether or not each of the candidacy
links selected by said selecting step is allowable according to
link judgement information, said link judgement information
including a connection relationship between each of the candidacy
links and the confirmed link connected to each of the candidacy
links, said link judgement information being set in advance;
and
a confirmation means for confirming one of the candidacy links
judged to be allowable by said judgement means, said confirmed link
having a shortest integrated route distance from the starting
position, said selection means selecting said candidacy links from
said confirmed links.
8. A navigation system according to claim 7, wherein said guidance
means comprises a display means for displaying the message.
9. A navigation system according to claim 7, wherein said guidance
means comprises a voice outputting means for outputting the message
by a synthetic voice.
10. A navigation system according to claim 7, further
comprising:
a measurement means for measuring a present position of said
movable body; and
a setting means for setting the destination,
said guidance means generating the message to guide said movable
body from the measured present position to the destination on the
obtained shortest route.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a route setting method
and a route setting apparatus in a navigation system, and more
particularly to a route setting method and a route setting
apparatus used in a car navigation system for performing a route
self-guidance of a vehicle to a destination. 2. Description of the
Related Art
There is a so-called "built-in type navigation apparatus" as a
measuring apparatus for various movable bodies such as a vehicle,
an airplane, a ship etc. This built-in type navigation apparatus is
constructed to obtain two dimensional displacement (i.e. a vector
amount) of the movable body from an azimuth data of an azimuth
sensor and speed data of a speed sensor and obtain a present
position by integrating this two dimensional displacement on a
standard point. Namely, in case of an automobile for example, it is
constructed such that the number of pulses which are generated
during one rotation of a drive shaft is set in advance, and that
the travel distance is obtained by multiplying a distance, which is
calculated from the total number of the pulses generated from the
standard point to the present position, by a distance correction
coefficient.
There is also a GPS (Global Positioning System) type navigation
apparatus as a measuring apparatus, which utilizes artificial
satellites. This GPS type navigation apparatus is constructed as
follows. Namely, it receives electric waves of three or more GPS
satellites normally, and calculates a present position of a
receiving point from the pseudo-distance data, which include a time
offset of a receiver between each GPS satellite and the receiving
point and the positional data of each GPS satellite. Then, an
information processing device reads out map data, which include the
calculated present position, from a map data storing device, to
take in the data. Then, the information processing device forms
image data from the taken-in map data and the information of the
present position, and sends it to the display device to perform the
image display. By this image, the automobile driver etc. who is a
user can recognize the present position in relation with the
map.
The above described navigation apparatus may perform not only a
display of a vehicle in the above described manner but also an
automatic route setting operation by inputting a starting position
and a destination, so as to guide a vehicle to the destination on
the basis of the automatically set shortest route.
In such an automatic route setting operation, as a method for
automatically performing the route setting operation, there is the
Dijkstra method.
The Dijkstra method determines the shortest route by determining a
node, which corresponds to a route position such as a crossing to
be routed, one after another from the small peripheral area around
the starting position (starting node), and gradually expands the
area for determining the node to finish the process at the time
when the shortest route to the destination (objective node) is
finally obtained.
The algorithm of the Dijkstra method is as following.
Namely, all of the nodes which are connected to the starting node
via links are set as candidacy nodes. Then, the node with the
minimum cost (link length is the minimum) is set as a confirmed
node. Then, all of the nodes which are connected to the confirmed
node via links are set as new candidacy nodes. However, in the
event that there is a node which has already been a candidacy node,
if the cost to the confirmed node is small, the route passing
through the confirmed node is adopted as the shortest route.
Finally, the above processes of setting the node and adopting the
route are repeated, and when the objective node coincides with the
confirmed node, the process is ended.
By this algorithm, the shortest route from the starting position to
the destination can be automatically obtained according to the
Dijkstra method.
However, according to the study and analysis conducted by the
inventors of the present application, this route setting method in
the navigation system by means of the Dijkstra method has a serious
drawback as explained hereinbelow with referring to FIG. 3 and FIG.
5.
FIG. 3 is a route diagram for explaining a concrete operation of
the route setting system.
In FIG. 3, it is assumed that the starting position is node A and
the destination is node G, the route of node D .fwdarw. node F
.fwdarw. node G cannot be adopted since the right turn is
prohibited thereon, and the U turn is also prohibited. Each numeral
represents a link length i.e. a distance between nodes.
FIG. 5 is a diagram for explaining a concrete operation of the
route setting system.
In FIG. 5, in the expression X (Y, Z), X represents the candidacy
node name, Y represents the previous node name before arriving at
the candidacy node X by one node, and Z represents the integrated
cost (integrated distance) up to the candidacy node X.
Firstly, the candidacy nodes obtained as for the node A which is
the starting position are nodes B and C. Since the node which has
the minimum cost among these candidacy nodes is the node B, the
node B is adopted as the confirmed node.
As a result, the node D which is connected to the node B is adopted
as the new candidacy node, and the candidacy nodes become the nodes
C and D. Since, among these candidacy nodes, the node which has the
minimum cost is the node C, the node C is adopted as the confirmed
node.
Successively, the node E which is connected to the node C is
adopted as the new candidacy node, and the candidacy nodes become
the nodes D and E. Since, among these candidacy nodes, the node
which has the minimum cost is the node D, the node D is adopted as
the confirmed node.
Further, node F which is connected to node E is adopted as the new
candidacy node, and the candidacy nodes become the nodes E and F.
Since, among these candidacy nodes, the node which has the minimum
cost is node F, node F is adopted as the confirmed node.
Here node E which is connected to node F has been already adopted
as the candidacy node. Since the cost becomes smaller in case of
reaching node E through node F, node E passing via node F is
adopted as the new candidacy node. Node H which is connected to
node F is also adopted as the candidacy node. On the other hand,
node G is not adopted as the candidacy node since the right turn is
prohibited on the route of node D .fwdarw. node F .fwdarw. node
G.
Although each of the candidacy nodes E and H has the minimum cost,
since, node E has been already adopted as the candidacy node in the
previous step, node E is adopted as the confirmed node because the
priority thereof is higher.
In the event that a plurality of nodes each having the minimum cost
are adopted simultaneously as the candidacy nodes, the node with
the smallest node number among these nodes is adopted as the
confirmed node. For example, if they are node A and node C, node A
is adopted as the confirmed node, and if they are node E and node
D, node D is adopted as the confirmed node.
There remains only node H, which is adopted as the confirmed
node.
In this manner, according to the study and analysis by the
inventors of the present application, in the above explained route
setting method by means of the Dijkstra method, there arises a case
where the node G, i.e. the destination, cannot be reached if the
traffic regulation etc. is considered, which is a serious problem
in the navigation system in a practical sense.
In addition, according to the study and analysis by the present
inventors of the present application, in the above explained
Dijkstra method, in order to express the traffic regulation
condition e.g. the right or left turn prohibition and the U turn
prohibition, it becomes necessary to express it by use of a
directional graph as shown in FIG. 6A. Thus, at the presence of a
crossing street, since the directional graph is employed, the data
amount required for the route setting operation is increased to be
four times as high as the case where only the non-directional graph
by use of data having no directional property (distance only) as
shown in FIG. 6B is employed, which is another serious problem of
the navigation system.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
route setting method and a route setting apparatus in a navigation
system, and a navigation system having the route setting apparatus,
which can certainly set a correct route to a destination even if
there exists a traffic regulation, while the data amount required
for the route setting operation is relatively small.
The above object of the present invention can be achieved by a
route setting method in a navigation system for obtaining a
shortest route from a starting position to a destination position,
including the steps of: selecting, out of links each corresponding
to a partial route connecting two route positions adjacent to each
other on a route, candidacy links each connected to one of
confirmed links which include a link corresponding to the partial
route connected to the starting position and which have been
confirmed; judging whether or not each of the candidacy links
selected by the selecting step is allowable according to link
judgement information, which corresponds to a connection
relationship between each of the candidacy links and the confirmed
link connected to each of the candidacy links and which is set in
advance; confirming one of the candidacy links judged to be
allowable by the judging step, which has the shortest integrated
route distance from the starting position, as a new confirmed link;
and repeating the selecting, judging and confirming steps with
respect to the confirmed links including the link most recently
confirmed.
According to the route setting method of the present invention, the
candidacy links are selected by the selecting step. Then, it is
judged whether or not each of the candidacy links is allowable
according to link judgement information by the judging step. Here,
the link judgement information corresponds to a connection
relationship between the candidacy link and the confirmed link
connected to each other, and is set in advance. Then, one of the
candidacy links which has the shortest integrated route distance is
confirmed as a new confirmed link. Finally, the selecting, judging
and confirming steps are repeated with respect to the confirmed
links including the new confirmed link.
Therefore, a link corresponding to a partial route which is
connected to the destination, is always adopted as a candidacy link
at any one of the steps until the link corresponding to the partial
route connected to the destination is confirmed, i.e. at any one of
the steps until the route setting process is ended. Here, since the
selecting, judging and confirming steps are performed on the link
base, the traffic regulation such as a right or left turn
prohibition (which is also determined on the link base) can be also
considered on the link base. By use of the process on the basis of
the link, it becomes possible to judge whether or not the right or
left turn is prohibited at each route position. Consequently, even
if there exists a right turn prohibited portion at the vicinity of
the destination for example, the shortest route can be still found
in the present invention.
In this manner, according to the route setting method of the
present invention, the shortest route to the destination can be
certainly set regardless of the kinds of the traffic
regulation.
Further, it is enough for the link judgement information to express
whether or not the combination of the confirmed link and the
candidacy link adjacent to each other can be adopted or not. Thus,
even if the traffic regulations are expressed by the link judgement
information, the data amount necessary for the link judgement
information can be very small as compared with the case of the
related art in which the directional graph is employed to express
the traffic regulations as in FIG. 6A.
In one aspect of the route setting method of the present invention,
the method may have the step of storing the link judgement
information into a memory device. In this case, relatively small
memory capacity is required for the memory device since the data
amount of the link judgement information is small.
In another aspect of the route setting method of the present
invention, the link judgement information may include an
information flag which indicates whether or not each of the links
in the corresponding connection relationship is allowable under a
traffic regulation thereof. In this case, the data amount can be
effectively saved because of the information flag.
The above object of the present invention can be also achieved by a
route setting apparatus in a navigation system for obtaining a
shortest route from a starting position to a destination position,
provided with: a selection device for selecting, out of links each
corresponding to a partial route connecting two route positions
adjacent to each other on a route, candidacy links each connected
to one of confirmed links which include a link corresponding to the
partial route connected to the starting position and which have
been confirmed; a judgement device for judging whether or not each
of the candidacy links selected by the selection device is
allowable according to link judgement information, which
corresponds to a connection relationship between each of the
candidacy links and the confirmed link connected to each of the
candidacy links and which is set in advance; and a confirmation
device for confirming one of the candidacy links judged to be able
to pass therethrough by the judgement device, which has the
shortest integrated route distance from the starting position, as a
new confirmed link, the selection device selecting with respect to
the confirmed links including the new confirmed link confirmed by
the confirmation device.
According to the route setting apparatus of the present invention,
the selection device selects the candidacy links, and the judgement
device judges whether or not each of the candidacy links is able to
pass therethrough according to link judgement information. Here,
the link judgement information corresponds to a connection
relationship between the candidacy link and the confirmed link
connected to each other, and is set in advance. Then, the
confirmation device confirms one of the candidacy links which has
the shortest integrated route distance from the starting position,
as a new confirmed link. The selection device selects with respect
to the confirmed links including the new confirmed link.
Therefore, a link corresponding to the partial route which is
connected to the destination, is always adopted as a candidacy link
at any one of the steps until the link corresponding to the partial
route connected to the destination is confirmed, i.e. at any one of
the steps until the route setting process is ended. Thus, the
shortest route to the destination can be certainly set according to
the route setting apparatus of the present invention.
Further, it is enough for the link judgement information to express
whether or not the combination of the confirmed link and the
candidacy link adjacent to each other can be adopted or not. Thus,
even if the traffic regulations are expressed by the link judgement
information, the data amount necessary for the link judgement
information can be very small.
In one aspect of the route setting apparatus of the present
invention, the judgement device may have a memory device for
storing the link judgement information in advance. In this case,
the link judgement information can be easily stored in advance.
In another aspect of the route setting apparatus of the present
invention, the link judgement information may include an
information flag which indicates whether or not each of the links
in the corresponding connection relationship is allowable under a
traffic regulation thereof. In this case, the data amount necessary
for the link judgement information can be effectively saved because
of the information flag.
The above object of the present invention can be also achieved by a
navigation system for a movable body provided with: the above
described route setting apparatus of the present invention; and a
guidance device for generating a message to guide the movable body
from the starting position to the destination on the basis of the
shortest route obtained by the route setting apparatus.
Thus, the aforementioned novel effect of the route setting
apparatus of the present invention can be realized in the same
manner according to the navigation system of the present
invention.
In one aspect of the navigation system of the present invention,
the guidance device may include a display device for displaying the
message. Thus, the operator can easily watch the message related to
the automatically set shortest route. Alternatively, the guidance
device may include a voice outputting device for outputting the
message by a synthetic voice. Thus, the operator can easily listen
to the message related to the automatically set shortest route.
In another aspect of the navigation system of the present
invention, the system may have a measurement device for measuring a
present position of the movable body, and a setting device for
setting the destination. The guidance device generates the message
to guide the movable body from the measured present position to the
destination on the obtained shortest route. Thus, the appropriate
route guidance along with the movement of the movable body can be
conducted.
The nature, utility, and further features of this invention will be
more clearly apparent from the following detailed description with
respect to preferred embodiments of the invention when read in
conjunction with the accompanying drawings briefly described
below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a construction of a navigation
apparatus as an embodiment of the present invention;
FIG. 2 is a flow chart showing an operation of the embodiment;
FIG. 3 is a route diagram for explaining a concrete operation of
the embodiment as well as the related art;
FIG. 4 is a diagram for explaining a concrete operation of the
embodiment;
FIG. 5 is a diagram for explaining a concrete operation of the
related art; and
FIGS. 6A-6B are the diagrams for explaining a difference in the
data amount between a directional graph and a non-directional
graph.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the accompanying drawings, a preferred embodiment of
the present invention will be now explained.
FIG. 1 is a block diagram showing a basic construction of an
on-vehicle navigation system as an embodiment of the present
invention.
In FIG. 1, the on-vehicle navigation system is provided with: a
geomagnetic sensor 1 for outputting azimuth data regarding the
direction of travel of a vehicle; an angular speed sensor 2 for
detecting an angular speed at the time of the rotation of the
vehicle and outputting angular speed data; a travel distance sensor
3 for outputting travel distance data by detecting and integrating
the number of rotations of a shaft; a GPS receiver 4 for receiving
electric waves from GPS satellites and outputting GPS measurement
data; a system controller 5 for controlling a whole navigation
system on the basis of the azimuth data, the angular speed data,
the travel distance data and the GPS measurement data; an input
device 11 for inputting various data; a CD-ROM (Compact Disk--Read
Only Memory) drive 12 for reading and outputting various data from
a CD-ROM disk DK under the control of the system controller 5; a
display unit 13 for displaying various display data under the
control of the system controller 5; and an audio reproducing unit
18 for reproducing and outputting various voice data under the
control of the system controller 5.
The system controller 5 is provided with: an interface unit 6 for
performing an interface operation with the external elements; a CPU
7 for controlling the whole portion of the system controller 5; a
ROM (Read Only Memory) 8 for storing a control program to control
the system controller 5; and a RAM (Random Access Memory) 9 having
a non-volatile memory not shown for storing various data in a
writable manner. The input device 11, the CD-ROM drive 12, the
display unit 13 and the audio reproducing unit 18 are connected via
a bus line 10.
The display unit 13 is provided with: a graphic controller 14 for
controlling the whole portion of the display unit 13 on the basis
of the control data from the CPU 7 which are transmitted through
the bus line 10; a buffer memory 15 consisting of a memory such as
a VRAM (Video RAM), for temporarily storing image information,
which can be immediately displayed; and a display control unit 16
for controlling the display of the display device 17 such as a
liquid crystal display device, a CRT (Cathode Ray Tube) on the
basis of the image data outputted from the graphic controller
14.
The audio reproducing unit 18 is provided with: a D/A converter 19
for performing a digital/analog conversion of audio voice digital
data transmitted through the bus line 10 from the CD-ROM drive 12
or the RAM 9; an amplifier 20 for amplifying an audio analog signal
outputted from the D/A converter 19; and a speaker 21 for
generating sound from the amplified audio analog signal.
In this case, it is assumed that link judgement data is read from
the CD-ROM disk DK into the RAM 9 in advance, and the system
controller 5 performs the selecting, judging and confirming the
candidacy links.
Next, the operation of the setting method of the present embodiment
is explained with referring to FIG. 2.
First, all links which are connected to the starting position
(departure point) are set as the candidacy links (step S20).
Successively, the system controller 5 determines or confirms one
link (hereinbelow, it is referred to as link LA), whose cost (i.e.
integrated cost which corresponds to the integrated distance from
the starting position) is the minimum, out of all candidacy links
(step S21).
Next, it is judged whether or not this link LA as a first link
reaches the destination (step S22). If it reaches the destination
(YES), the process is ended.
In the judgement in the step S22, if the link LA does not reach the
destination (NO), the data with respect to the links connected to
link LA, including the link judgement data as for the link LA, are
obtained (step S23).
From the data as for the link LA, the total number n of the links
connected to link LA is set to the counter C (step S24).
Successively, it is judged whether or not the vehicle is able to
proceed to a road corresponding to the link which is expressed by
the counter C on the basis of the link judgement data i.e., whether
or not the link expressed by the counter C can be adopted as a
candidacy link under the traffic regulation thereof (step S25).
By the judgement at the step S25, if the link expressed by the
counter C cannot be adopted as a candidacy link (NO), the counter C
is counted-down, so that the process of the step S25 is performed
again (step S29).
By the judgement at the step S25, if the link expressed by the
counter C can be adopted as a candidacy link (YES), it is judged
whether or not the link expressed by the counter C is a confirmed
link (step S26).
By the judgement at the step S26, if the link expressed by the
counter C is a confirmed link (YES), the counter C is counted-down,
so that the process of the step S25 is performed again (step
S29).
By the judgement at the step S26, if the link expressed by the
counter C is not a confirmed link (NO), it is judged whether or not
the pertinent link is a candidacy link (step S27).
By the judgement at the step S27, if the link expressed by the
counter C is not already a candidacy link (NO), the link expressed
by the counter C is adopted and registered as a new candidacy link
(step S28), and the counter C is counted-down, so that the process
of the step S25 is performed again (step S29).
By the judgement at the step S27, if the link expressed by the
counter C is already a candidacy link (YES), and in case that the
integrated cost associated with the candidacy link becomes smaller
if the link LA is passed through (i.e., if is adopted), the link LA
the integrated cost associated with this candidacy link is
rewritten to reflect connection via the link LA (step S30).
After that, the processes from the step S24 to the step 29 are
performed n times on the basis of the counter C (step S29), and it
returns to the process at the step S21, so that the process is
performed until the new link LA reaches the destination.
By constructing in the above described manner in which the route
are selected, judged and confirmed by the unit of link i.e. not by
the unit of node as in the aforementioned Dijkstra method of the
related art, even if the traffic regulations are considered, the
shortest route can be certainly obtained which reaches the
destination.
Nextly, the route setting method of the present embodiment is more
concretely explained with referring to FIG. 3 and FIG. 4.
FIG. 3 is a route diagram for explaining a concrete operation of
the route setting system.
In FIG. 3, it is assumed that the starting position is the node A,
the destination is the node G, the route of node D .fwdarw. node F
.fwdarw. node G cannot be adopted since the right turn is
prohibited thereon, and that the U turn is also prohibited. Each
numeral represents a link length or a distance between nodes.
FIG. 4 is a diagram for explaining a concrete operation of the
route setting system.
In FIG. 4, the expression X (Y, Z) expresses a link number X of a
candidacy link (including a directional property), a link number Y
of a link which has been already confirmed one step before the
candidacy link of the link number X, and an integrated cost Z
(integrated distance) from the starting position to the end of the
candidacy link of the link number X through the link of the link
number Y. The definitions of the link numbers 1 to 16 are shown in
the lower portion of FIG. 4.
More concretely, the expression 4 (1, 3) in the candidacy link
column of the table of FIG. 4 for example, expresses that: the link
from the node B to the node D (which link number="4") is adopted as
the candidacy link; the link before this adopted candidacy link is
the link from the node A to the node B (which link number="1"), and
that the integrated cost from the starting position to the node D
through these links (with link numbers=1 and 4) is "3".
In the explanation below, a link from the node A to the node B is
expressed as a "link A .fwdarw. B", and a link from the node B to
the node A is expressed as a "link B .fwdarw. A" conversely. Other
links are also expressed in the same manner.
First, the node A, the starting position, is set as the confirmed
node. The obtained candidacy links are the link A .fwdarw. B having
the link number=1 (corresponding to 1(0,1)) and the link A .fwdarw.
C having the link number=2 (corresponding to 2(0,2)). Among these
candidacy links, the link which has the minimum cost is the link A
.fwdarw. B (cost=1). Thus, the link A .fwdarw. B is set as the
confirmed link (step S1).
As a result, the link B .fwdarw. D having the link number=4 which
is connected to the node B is newly adopted as the candidacy link
(corresponding to 4(1,3)). Thus, the link A .fwdarw. C and the link
B .fwdarw. D become the candidacy links. The link which has the
minimum cost among these candidacy links is the link A .fwdarw. C
(cost=2), so that the link A .fwdarw. C is set as the confirmed
link (step S2). In this case, the link B .fwdarw. A (link number=3)
is not adopted as the candidacy link since it represents a U
turn.
Successively, the link C .fwdarw. E having the link number=6 which
is connected to the node C is newly adopted as the candidacy link
(corresponding to 6(2,6)). The link B .fwdarw. D and the link C
.fwdarw. E become the candidacy links. The link which has the
minimum cost among these candidacy links is the link B .fwdarw. D
(cost=3), so that the link B .fwdarw. D is set as the confirmed
link (step S3).
Further, the link D .fwdarw. F having the link number=8 which is
connected to the node D is newly adopted as the candidacy link
(corresponding to 8(4,4)). Thus, the link C .fwdarw. E and the link
D .fwdarw. F become the candidacy links. The link which has the
minimum cost among these candidacy links is the link D .fwdarw. F
(cost=4), so that the link D .fwdarw. F is set as the confirmed
link (step S4).
Next, the link F .fwdarw. E having the link number=12 and the link
F .fwdarw. H having the link number=14 which are connected to the
node F are newly adopted as the candidacy links (corresponding to
12(8,5) and 14(8,5) respectively). Thus, the links C .fwdarw. E,
the link F .fwdarw. E and the link F .fwdarw. H become the
candidacy links. In this case, the link F .fwdarw. D having the
link number=11 which is connected to the node F is not adopted
since it represents a U turn, and the link F .fwdarw. G having the
link number=13 is not adopted since it comes under the traffic
regulation of the right turn prohibition on the basis of the link
judgement data.
Although both the link F .fwdarw. E (cost=5) and the link F
.fwdarw. H (cost=5) have the minimum cost among these candidacy
links, the link F .fwdarw. E is set as the confirmed link, since
the link whose link number is the minimum is set as the confirmed
link in the case that a plurality of candidacy links are adopted as
the link having the minimum cost (step S5).
Successively, the link E .fwdarw. C having the link number=9 which
is connected to the node E is newly adopted as the candidacy link
(corresponding to 9(12,9)). Thus, the link C .fwdarw. E, the link F
.fwdarw. H and the link E .fwdarw. C become the candidacy links.
The link which has the minimum cost among these candidacy links is
the link F .fwdarw. H (cost=5), so that the link F .fwdarw. H is
set as the confirmed link (step S6).
Here, since there is no link connected to the node H, the link
which has the minimum cost among the remained candidacy links is
the link C .fwdarw. E (cost=6), so that the link C .fwdarw. E is
set as the confirmed link (step S7).
Next, the link E .fwdarw. F having the link number=10 which is
connected to the node E is newly adopted as the candidacy link
(corresponding to 10(6,7)). Thus, the link E .fwdarw. C and the
link E .fwdarw. F become the candidacy links. The link which has
the minimum cost among these candidacy links is the link E .fwdarw.
F (cost=7), so that the link E .fwdarw. F is set as the confirmed
link (step S8).
Further, the link F .fwdarw. D having the link number=11 and the
link F .fwdarw. G having the link number=13 which are connected to
the node F are newly adopted as the candidacy link (corresponding
to 11(10,8) and 13(10,8) respectively). Thus, the link E .fwdarw.
C, the link F .fwdarw. D and the link F .fwdarw. G become the
candidacy links. Although both the link F .fwdarw. D (cost=8) and
the link F .fwdarw. G (cost=8) have the minimum cost among these
candidacy links, the link F .fwdarw. D is set as the confirmed
link, since the link whose link number is the minimum is ruled in
the present embodiment to be set as the confirmed link in the event
a plurality of candidacy links are adopted as the link having the
minimum cost (step S9). As an alternative, the link, whose link
number is the maximum in place of the minimum may be set as the
confirmed link depending on the manner of assigning the link
numbers to the links.
On the other hand, in the event a plurality of links are adopted as
the candidacy links each having the minimum cost and that there is
one link which has been already adopted as the candidacy link in
the process steps preceding the previous step, the link which has
been adopted as the candidacy link in the earliest process step is
set as the confirmed link.
In addition, it is possible to construct the apparatus such that
the processes are ended by judging whether or not the link F
.fwdarw. G reaches the node G which is the destination in this
case.
In this case, since the link F .fwdarw. E (link number=12) has been
already confirmed at the step S5 and the link F .fwdarw. H (link
number=14) has been also already confirmed at the step S6, they are
not adopted.
Successively, the link D .fwdarw. B having the link number=7 which
is connected to the node D is newly adopted as the candidacy link
(corresponding to 7(11,10)). Thus, the link E .fwdarw. C, the link
F .fwdarw. G and the link D .fwdarw. B become the candidacy links.
The link which has the minimum cost among these candidacy links is
the link F .fwdarw. G (cost=8), so that the processes are ended
since the shortest route to the node G which is the destination is
confirmed.
As a result, the combination of the links from the node A, which is
the starting position, to the node G, which is the destination, is
the link A .fwdarw. C (link number=2), the link C .fwdarw. E (link
number=6), the link E .fwdarw. F (link number=10) and the link F
.fwdarw. G (link number=13), and the integrated cost thereof
becomes "8".
As explained above, according to the present embodiment, a link,
which is connected to the node corresponding to the destination, is
always adopted as a candidacy link at any one of the steps until
the link connected to the node corresponding to the destination is
confirmed i.e. at any one of the steps until the route setting
process is ended. Here, since the selecting, judging and confirming
steps are performed on the link base, the traffic regulation such
as a right or left turn prohibition (which is also determined on
the link base) can be also considered on the link base. This is
very different from the aforementioned route setting method by
means of the Dijkstra method, in which the selecting, judging and
confirming steps are performed on the node base, and in which it is
not possible to judge whether the route at the node is turned right
or left by use of the process on the basis of the node without the
large amount of data indicating the directional graph of FIG. 6A
while the data as for the route up to the pertinent node is
discarded. On the contrary, in the present embodiment, by use of
the process on the basis of the link, it becomes possible to judge
whether the route at each node is turned right or left.
Consequently, even if there exists a right turn prohibited portion
at the vicinity of the destination for example, the shortest route
can still be found in the present embodiment. In this manner,
according to the route setting method and apparatus of the present
embodiment, the shortest route to the destination can be certainly
and easily set even if the traffic regulations etc. are
considered.
Further, it is enough for the link judgement information to express
whether or not the combination of the confirmed link and the
candidacy link adjacent to the confirmed link can be adopted or
not. In other words, it is not necessary to store the link
judgement information with respect to one whole route consisting of
a plurality of links, but it is only necessary to store the link
judgement information with respect to each pair of the links
adjacent to each other. Thus, even if the traffic regulations are
expressed by the link judgement information, the data amount
required for the expression is relatively small as compared with
the original link data amount, and the capacity of the recording
medium or the memory etc., can be also restrained.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
present embodiments are therefore to be considered in all respects
as illustrative and not restrictive, the scope of the invention
being indicated by the appended claims rather than by the foregoing
description and all changes which come within the meaning and range
of equivalency of the claims are therefore intended to be embraced
therein.
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